Copolymers of vinyl-functional monomers that are useful, for example, as adhesives, can be produced by bulk (i.e. solvent-free) free-radical (co)polymerization of a de-aerated (e.g. by sparging with an inert gas) monomer mixture in a batch reactor under essentially adiabatic reaction conditions (see, for example, U.S. Pat. No. 5,986,011). Polymerization typically involves the use of an added compound (i.e. an “initiator”) that starts the reaction of and subsequent chain formation by such vinyl-functional monomers. When free-radical initiators are used, the initiation step typically consists of two reactions. In the first reaction, the initiator undergoes cleavage or dissociation upon exposure to an energy source (e.g., heat, ultraviolet light, etc.), causing the formation of at least one radical species of the initiator. In a second step, this radical then combines with a first monomer to form a chain initiating species of the polymer. Once formed, this chain initiating radical propagates the polymerization reaction, incorporating other monomers into a growing polymer chain.
When heat is used as the source of energy to initiate polymerization of free-radically-reactive monomers, thermal initiators such as azo-compounds are typically added to the reactor. When ultraviolet radiation is the source of energy used to initiate free radical polymerization of reactive monomers, photoinitiators that absorb light and form radical species when exposed to energy in the ultraviolet to visible range (250 to 700 nm) are typically employed. Alternatively, electron-beam (e-beam) radiation may be used as the source of energy to initiate (co)polymerization without adding a thermal initiator or a photoinitiator to induce formation of radical species.